324 Dr Eschricht*s Inquiries concerning 



has lately been most accurately described, is that of the Pen- 

 tastoma. (Diesing, in the Annals of the Vienna Museum, 

 vol. i.) Concerning the Trematoda, numerous beautiful mo- 

 nographies have long since sufficiently proved our assertion, 

 every one being familiar w^ith the treatises of Mehlis, Laurer, 

 Nordmann, and Diesing. The Acantocephali have had a dili- 

 gent describer in Westrumb,andthe J?fA««(?r%wc/iM5^?^a5, par- 

 ticularly in Jules Cloquet. Of the Cestoidea the genus Both- 

 riocephalus has been carefully described by Professor Leuck- 

 art, and the Twnia solium by several anatomists, though not in 

 distinct monographies. In the year 1837 I had the honour 

 to receive the prize avrarded to a treatise upon the anatomy 

 and physiology of the Bothriocephalic by the Academy of Ber- 

 lin. It was sent in the month of May 1838 to the Academia 

 Caesarea Leopoldino-Carolina at Breslau, in order to be pub- 

 lished in its Acta ; and here I shall only notice, that this ani- 

 mal has a very complicated structure in each of its thousand 

 joints, very analogous to the structure of the Trematad. The 

 organs of generation I shall have an opportunity of describing 

 somewhat more particularly in the following pages. It is only 

 in the vesicular worms that a more complete internal struc- 

 ture has not yet been demonstrated, although important and 

 highly interesting notices have been furnished by Dr Siebold 

 (in Burdach's Physiology, 2d edit. vol. ii. p. 183-213). Fi- 

 nally, in respect to the third point, it is a general opinion that 

 the intestinal worms produce eggs and young ones, and the 

 accuracy of this opinion will also be amply illustrated in the 

 following pages. 



We have now to consider how far these restrictions may be 

 deemed compatible with the theory of equivocal generation, 



CHAP. II. IS CONSTANCY IN EXTERNAL FORM AND INTERNAL 



STRUCTURE COMPATIBLE WITH THE THEORY OF SPONTANE- 

 OUS GENERATION ? 



Sect. 1. It does not refute the Theory. — The question here 

 proposed might be answered in the affirmative, inasmuch as it 

 must be granted as a general law in nature, that forms in ge- 

 neral are confined within certain impassable limits, although the 

 necessity of this limitation transcends our conception. Thus, for 



